Automobile audio system

ABSTRACT

The invention features a dual-mode audio system for an automobile which in one mode is configured for play while the doors to the automobile are closed, and in a second mode, is configured for play while a door, such as a tailgate, is opened. Additionally, the invention also features a battery monitor which monitors the operating condition of the battery and may estimate the energy capacity of the battery. The system may also take power conservation measures if the system determines that the engine is not running or the operating condition of the batter reaches a predetermined state. The invention also features a remote control integrated within a key fob for controlling the audio system. The invention features various orientations for mounting a pair of loudspeakers within an automobile which directly radiate sound out of a rear opening of the automobile.

TECHNICAL FIELD

[0001] This invention relates to audio systems, and more particularly toaudio systems for automobiles.

BACKGROUND

[0002] Audio systems are included in virtually every automobilemanufactured today. These audio systems are typically designed for usewhile the doors, tailgates, and other openings to the passengercompartment are closed. However, people often choose to listen to theirautomobile audio system while they are outside of their vehicle, such aswhile they are camping or “tailgating” at a sporting event. Becausetraditional automobile audio systems are not designed for this type ofuse, listeners may not enjoy as high a quality sound presentation asthey could if the system were designed for outdoor use.

[0003] The acoustic characteristics of a typical vehicle with all of itsdoors closed will generally be significantly different than the acousticcharacteristics of the same vehicle with its tailgate (or one of itsdoors) open. For example, the linear transfer function from each speakerelement to various listening locations will be markedly different ineach circumstance. Furthermore, opening or closing of the tailgatesignificantly alters the acoustic characteristics of the cabin space.

[0004] Accordingly, it is desirable to have an automobile audio systemwhich is able to operate in two modes: one mode where one or moreparameters of the audio system are configured to better optimize soundquality while the doors (to include tailgates) are closed and a secondmode where one or more parameters of the audio system are configured tobetter optimize sound quality while one or more of the doors, such as atailgate, are open.

[0005] Additionally, users may wish to operate their automobile audiosystem while the engine is not running and thus drain power from theautomobile's battery. It is therefore desirable for an automobile audiosystem to monitor one or more operating conditions of the battery andadjust system performance in order to extend the maximum period of timethe audio system can operate from battery power. It is also desirable tomonitor one or more operating conditions of the battery to ensureoperation of the audio system does not result in a condition wheresufficient battery charge (to allow the automobile to be restarted) isno longer available.

[0006] It should be noted that the terms automobile and vehicle are usedsynonymously in this description and refer to any self-propelledpassenger vehicle used for land transport, including cars, trucks,pick-up trucks, sport utility vehicles, and the like. Additionally, theterm tailgate refers to a hinged door of an automobile which providesaccess to a rear opening of the automobile. A tailgate may be hingedlyconnected to the top, bottom, or side of the frame of the automobile.

SUMMARY

[0007] According to an aspect of the invention, a system and method foroperating an audio system in an automobile includes implementing a firstsystem configuration, receiving an input indicating a change inoperating mode, and in response to this input, implementing a secondsystem configuration which is different from the first systemconfiguration, wherein the second system configuration is implementedwhen one of the doors, such as a tailgate, of the automobile is open.

[0008] Embodiments include one or more of the following features. Thefirst system configuration may occur when all of the doors of theautomobile are closed and the second configuration may occur when one ormore of the doors, such as a tailgate, are opened.

[0009] The audio system may implement a different system topology in thefirst and second system configurations, where the system topologydefines how different signals provided by an audio source are routed tothe different speakers of the audio system.

[0010] The audio system may implement different signal processingoperation in the first and second system configurations. The differentsignal processing operations in the first and second systemconfigurations may include different equalization signal processingoperations, amplification operations, dynamic range control operation,or spatial enhancement operations.

[0011] The audio system may also receive input indicating that theautomobile's engine is not running, and, in response to this input, thefirst or second system configuration may be adjusted in order to reducepower consumption of the system. Several adjustments may be made to thefirst or second system configuration to reduce power consumptionincluding turning off one or more speakers (e.g., by muting the outputof the amplifier, placing the amplifier in standby mode, reducing thevoltage of the audio signal input to the amplifier to approximatelyzero, disconnecting the one or more loudspeakers from the amplifier,removing electrical power from the amplifier); reducing the gain in oneor more of the signal paths; controlling the maximum output power levelof the audio system (e.g., by dynamically adjusting the gain of avariable gain element as a function of a detected level of an audiosignal); or changing one or more other signal processing operations inthe first or second system configuration.

[0012] The audio system may switch between the first and second systemconfiguration by monitoring one or more physical conditions of theautomobile (e.g., whether a door is opened, the engine is running, or anoccupant is in the automobile) and generate a switch command based on achange in one or more of the monitored physical conditions. The audiosystem may provide a manual switch accessible to a user and changebetween system configurations based on the state of the switch. Themanual switch may be located on a remote control device (e.g., a keyfob) or mounted at one or more locations within the automobile (e.g., ona front or rear control panel).

[0013] The audio system may also include a battery monitoring processwhich receives input indicating one or more operating conditions of thebattery (e.g., the battery voltage, discharge current, temperature). Thebattery monitoring process may compare one or more of the monitoredoperating conditions to a predetermined state, and if the monitoredoperating conditions reach the predetermined state, then the systemwould take a responsive action such as triggering an alarm or reducingthe power consumption of the audio system. The battery monitoringprocess may further estimate the remaining capacity of the battery basedon one or more of the monitored operating conditions and compare theestimated capacity to a predetermined value, and, if the estimatedcapacity reaches or falls below the predetermined value, then the systemmay take a response action such as triggering an alarm or reducing thepower consumption of the audio system.

[0014] In another aspect, the invention features a method for remotelycontrolling an audio system in an automobile with a key fob having aplurality of buttons which includes defining a first set of commandscorresponding to each button on the key fob, wherein the first set ofcommand includes a command to actuate the door locks. The method alsoincludes defining a second set of commands corresponding to each button,wherein the second set of commands includes one or more commands forcontrolling the audio system of the automobile. The method furtherincludes switching between the first and second sets of commands basedon a predetermined condition.

[0015] Embodiments may include one or more of the following features.The key fob may include a switch having two states, and thepredetermined condition is a state of the switch. The audio system mayhave a first mode of operation and a second mode of operation and thepredetermined condition is the state of the mode of operation of theaudio system, such that the first set of commands are valid when theaudio system is in the first mode of operation and the second set ofcommands are valid when the audio system is in the second mode ofoperation.

[0016] In another aspect, the invention features a system and method foroperating an audio system in a vehicle with a battery that includesmonitoring one or more operating conditions of the battery, comparingone or more of the monitored conditions of the battery to apredetermined state, if the monitored operating conditions of thebattery reaches the predetermined state, then triggering an alarm.

[0017] Embodiments may include one or more of the following features.The alarm may be an audible alarm, visual alarm, or tactile alarm. Oneor more of the monitored operating conditions of the battery may includesensing the output voltage level of the battery, sensing the dischargecurrent of the battery; or sensing the ambient temperature.

[0018] In another aspect, the invention features a system and method foroperating an audio system in a vehicle with a battery that includesmonitoring one or more operating conditions of the battery, comparingone or more of the monitored conditions of the battery to apredetermined state, and if the monitored operating conditions of thebattery reaches the predetermined state, then causing the automobile tostart its engine.

[0019] In another aspect, the invention features a system and method foroperating an audio system in a vehicle with a battery that includesmonitoring one or more operating conditions of the battery, comparingone or more of the monitored conditions of the battery to apredetermined state, and if the monitored operating conditions of thebattery reaches the predetermined state, then turning off a subset ofthe plurality of speakers.

[0020] In another aspect, the invention features a system and method foroperating an audio system in a vehicle with a battery that includesmonitoring one or more operating conditions of the battery, comparingone or more of the monitored conditions of the battery to apredetermined state and if the monitored operating conditions of thebattery reaches the predetermined state, then adjusting one or more ofequalization signal processes to change the frequency response of theaudio system.

[0021] In another aspect, the invention features a system and method foroperating an audio system that includes monitoring one or more operatingconditions of the battery, comparing one or more of the monitoredconditions of the battery to a predetermined state, and if the monitoredoperating conditions of the battery reaches the predetermined state,then detecting the level of one or more of audio signals received froman audio source, and dynamically adjusting the gain of one or morevariable gain elements as a function of the level of one or more audiosignals received from an audio source.

[0022] In another aspect, the invention features a system and method foroperating an audio system that includes monitoring one or more operatingconditions of the battery, estimating the remaining capacity of thebattery based on one or more of the monitored operating conditions ofthe battery, comparing the estimated remaining capacity of the batteryto a predetermined value; and, if the estimated remaining capacity ofthe battery is equal to or less than a predetermined value, then causingthe audio system to take an action.

[0023] Embodiments may include one or more of the following features.The action taken by the audio system in response to reaching or fallingbelow the predetermined value may include triggering an alarm, causingthe automobile to start the engine, or reducing the power consumption ofthe audio system (e.g., by turning off one or more loudspeakers, turningoff the system, adjusting one or more equalization processes applied toone or more audio signals to change the frequency response of the audiosystem).

[0024] In another aspect, a system and method for operating an audiosystem in an automobile includes determining whether the engine isrunning, and, in response to the system determining that the engine isnot running, then changing one or more signal processes to reduce powerconsumption of the audio system.

[0025] Embodiments may include one or more of the following features.The system may reduce power consumption in various ways including byturning off one or more speakers, adjusting one or more of theequalization processes performed on one or more of the received audiosignals to change the frequency response of the audio system, reducingthe gain in one or more of the audio signal paths.

[0026] In another aspect, an audio system for an automobile includes anaudio input source, a plurality of loudspeakers, a first set ofoperating conditions for a first mode of operation, a second set ofoperating conditions for a second mode of operation, wherein the secondset of operating conditions is different from the first set of operatingconditions and occurs when one of the doors of the automobile is open,and a switch for changing between the first and second set of operatingconditions.

[0027] Embodiments may include one or more of the following features.The first set of operating conditions are configured for play while atailgate is closed and listeners are within the automobile and thesecond set of operating conditions are configured for play while atailgate is open and listeners are outside the automobile. The audiosystem may also include at least one channel of equalization, whereinthe first set of operating conditions defines a first frequency responseof the channel of equalization and the second set of operatingconditions defines a second frequency response of the channel ofequalization. The audio system may also include a dynamic range controldevice configured to receive an audio signal having a first dynamicrange and output an audio signal having a second dynamic range, whereinthe second dynamic range is different than the first dynamic range. Thesystem may also include a battery monitoring process.

[0028] The audio system may also include a rear control panel locatedwithin the passenger compartment of the automobile towards the back ofthe automobile that includes one or more controls for operating theaudio system. The rear control panel may include a switch for changingbetween the first and second set of operating conditions. The rearcontrol panel may also include at least one pair of external audiosource line level inputs, an external microphone level input, or aseparate video output jack for connection to a video display.

[0029] In another aspect, the invention features an audio system for anautomobile having a passenger compartment and a tailgate hingidlyconnected to the top portion of the automobile's frame that includes afirst speaker set having a first speaker and a second speaker. The firstand second speakers are mounted on the tailgate of the automobile suchthat each speaker directs sound along a primary axis of radiation andhas a fixed orientation such that each speaker's primary axis ofradiation directs sound substantially towards the passenger compartmentof the automobile when the tailgate is closed, and the speaker's primaryaxis of radiation is pointed away from the passenger compartment of theautomobile and is angled relative to the plane of the ground when thetailgate is opened.

[0030] Embodiments may include one or more of the following features.The speakers may be mounted near an upper edge of the tailgate, forexample, on the window of the tailgate.

[0031] The audio system may be have a first mode of operation configuredfor play while the tailgate is closed and listeners are within theautomobile and a second mode of operation configured for play while thetailgate is opened and listeners are outside the automobile near therear of the automobile. The audio system may also have a second set ofspeakers that includes a first and second speaker, and mounted such thateach speaker having primary axis of radiation that is pointedsubstantially towards the rear of the automobile and which direct soundoutside the automobile in the second mode of operation.

[0032] In another aspect, an audio system for an automobile having apassenger compartment and a tailgate hingidly connected to theautomobile's frame and a rear seat or seats having a front portion and arear portion includes first speaker set that includes a first speakerand a second speaker. The first speaker set is mounted on the rearportion of the rear seat or seats, such that each speaker in the firstset of speakers directs sound along a primary axis of radiation and hasa fixed orientation such that each speaker's primary axis of radiationdirects sound substantially away from the passenger compartment of theautomobile towards the tailgate when the tailgate is closed, and thespeaker's primary axis of radiation is pointed away from the passengercompartment of the automobile and directs sound out of the rear of theautomobile when the tailgate is opened.

[0033] In another aspect, an audio system for an automobile having arear seat, a passenger compartment with a floor, and a tailgate hingidlyconnected to the automobile's frame includes a first speaker setcomprising a first speaker and a second speaker. The first speaker setis mounted on the floor, wherein each speaker in the first set ofspeakers directs sound along a primary axis of radiation and has a fixedorientation such that each speaker's primary axis of radiation directssound substantially away from the passenger compartment of theautomobile towards the tailgate when the tailgate is closed, and thespeaker's primary axis of radiation is pointed away from the passengercompartment of the automobile and directs sound out of the rear of theautomobile when the tailgate is opened.

[0034] In another aspect, an audio system for an automobile having arear seat, a passenger compartment with a ceiling, and a tailgatehingidly connected to the automobile's frame includes a first speakerset comprising a first speaker and a second speaker. The first speakerset is mounted on the ceiling, wherein each speaker in the first set ofspeakers directs sound along a primary axis of radiation and has a fixedorientation such that each speaker's primary axis of radiation directssound substantially away from the passenger compartment of theautomobile towards the tailgate when the tailgate is closed, and thespeaker's primary axis of radiation is pointed away from the passengercompartment of the automobile and directs sound out of the rear of theautomobile when the tailgate is opened.

[0035] In another aspect, an audio system for an automobile having apassenger compartment with a ceiling, floor, and sidewalls, and having arear opening includes a first speaker set comprising a first speaker anda second speaker. The first speaker set is mounted within the passengercompartment in the rear half of the automobile (e.g., on the floor orceiling), wherein each speaker in the first set of speakers directssound along a primary axis of radiation and has a fixed orientation suchthat each speaker's primary axis of radiation direct sound substantiallytowards the rear opening of the automobile and wherein the neitherspeaker in the first speaker set is mounted on a sidewall of thepassenger compartment.

[0036] The details of one or more embodiments of the invention are setforth in the accompanying drawings and the description below. Otherfeatures, objects, and advantages of the invention will be apparent fromthe description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0037]FIG. 1A is a is a top view of an automobile having a dual-modeaudio system.

[0038]FIG. 1B is a top view of an automobile having another dual modeaudio system.

[0039]FIG. 2A is a flow-chart illustrating the operation of a modedetection process in a dual-mode audio system.

[0040]FIG. 2B is a flow-chart illustrating the operation of a modedetection process in a tri-mode audio system.

[0041]FIG. 3 is a flow-chart illustrating the operation of a batterymonitoring process in a dual-mode audio system.

[0042]FIG. 4 is a diagram of a sport utility vehicle having a rear setof controls and rear speakers mounted on its tailgate.

[0043] FIGS. 5A-5D are side views of an automobile having rear speakersmounted in four different locations.

[0044] Like reference symbols in the various drawings indicate likeelements.

DETAILED DESCRIPTION

[0045] As shown in FIG. 1A, an automobile (e.g., an SUV) 10 includes anaudio system 20 that is configured to operate in two modes: aconventional mode and an open mode.

[0046] The conventional mode is a mode of operation in which audiosystem 20 is configured for play when all of the doors of the vehicleare closed and the primary listening position of interest is the seatingarea within the passenger compartment. In this mode, sound is radiatedwithin the passenger compartment as in a conventional automobile audiosystem.

[0047] The open mode is a mode of operation in which audio system 20 isconfigured for play when the tailgate 11 is open. In this mode, sound isradiated through the open tailgate and/or through the vehicle's bodypanels or other openings to the outside environment. The primarylistening position of interest in this case is outside of the vehicle,typically in line with the open tailgate 11. In other embodiments, theopen mode of operation may be configured for play when one or more doors(including a tailgate) are open.

[0048] Because the acoustic characteristics of the vehicle aresignificantly different when all of the doors are closed versus when oneor more doors are opened, and because the listening positions of primaryconcern are different in the different modes, the audio system 20adjusts system configuration in order to better optimize performance ineach mode. As will be explained in greater detail below, adjustment ofsystem configuration may include altering the system topology for eachmode of operation, as well as performing different signal processingoperations such as equalization, signal mixing, amplification, dynamicrange control, spatial enhancement processes and other signal processingtechniques on the channels of audio data in each mode of operation. Thesystem topology defines how different signals provided by an audiosource are routed to the different speakers of the audio system.

[0049] Additionally, audio system 20 features a battery monitoringprocess which monitors one or more operating conditions of theautomobile battery 30 and takes one or more actions based on whether thesystem 20 is primarily running off of the battery and the state of oneor more of the monitored operating conditions. As will be explained ingreater detail below, the battery monitoring process takes variousactions including triggering an alarm and altering the systemconfiguration in order to conserve battery power.

[0050] Referring again to FIG. 1A, audio system 20 includes one or moreaudio sources (not shown) such as a stereo radio, CD player, DVD player,and/or an MP3 player, which may be mounted in or near a front controlconsole 21, a rear control console 22, or at another location within theautomobile 10. The front and rear control consoles 21, 22 each maycontain a set of controls (e.g., volume, source selection, trackselection, play, pause, etc.) for the audio sources included within thesystem 20.

[0051] Audio system 20 also includes two pair of front speakers 24 a-24b, 24 c-24 d, a pair of side speakers 26 a-26 b, a pair of rear speakers28 a-28 b, and a woofer 29.

[0052] It should be noted that the arrangement of elements, as well asthe number of elements shown in FIG. 1A, were chosen to illustrate thenovel features of the invention. It should be understood that theinvention is not limited to use of the particular configuration ofspeaker elements and placements shown. For example, as shown in FIG. 1B,another dual-mode audio system 20′ may include a front center speaker25′ located in the dashboard of the automobile 10′ and a rear centerspeaker 23′ located near the rear of the passenger's compartment in thevehicle.

[0053]FIGS. 2A and 3 illustrate operation of the audio system 20 shownin FIG. 1A.

[0054] As shown in FIG. 2A, the audio system 20 includes a modedetection process 100 which detects when the system 20 is turned on 102and when a switching event 108, 114 occurs. A switching event occurswhen a user changes the state of a switch provided within the system 20.One or more manual switches may be located on the front control panel 21(shown in FIG. 1A), rear control panel 22, on a remote control device,on a key fob, or in another location. Since it is possible thatsignificant changes would be made in system operation when the mode ischanged, having a manual switch keeps from dramatically changing systemoperation while passengers remain inside the vehicle.

[0055] In other embodiments, a switching event may occur automatically.For example, a switching event may occur automatically when the systemdetects that a tailgate or door is open and the vehicle engine is notrunning (which can be sensed by the state of the ignition interlock, theRPM of the engine, or some other means). It may also be desirable tosense if passengers remain in the vehicle cabin, which could be doneusing seat switches, ultrasonic motion detectors, or some other method.Thus, in other embodiments, the system may automatically switch modes tothe open mode when the tailgate or door is open, the engine is off, andno passengers are occupying the vehicle cabin.

[0056] Referring again to FIG. 2A, when the mode detection process 100detects that the system 20 has been turned on 102, the process 100 willplace the system in a conventional mode of operation 104. Byautomatically reverting to a conventional mode when the system is turnedon, the system avoids a situation where the driver gets into the vehicleand turns on the system after it had been switched to open mode.However, in other embodiments, a mode detection process in a dual-modeaudio system could be configured to start up in different modesdepending on how the system was turned on or the state of a switch. Forexample, if the system was turned on using controls mounted in the frontof the vehicle, the system may assume that someone would be inside thevehicle and the system should start in conventional mode. If the systemwere turned on using controls that were easily accessible from outsidethe vehicle (such as controls located in rear console 22, or controlslocated on a remote control), the system may be configured to start upin open mode.

[0057] When the system 20 is placed in the conventional mode ofoperation 104, the system 20 is in a first system configuration 106which, as will be explained in more detail below, has a first systemtopology and performs a first set of signal processing operations whichare configured for play with the doors of the vehicle closed and theprimary listening position within the passenger's compartment. Thesystem 20 remains in its first system configuration 106 until aswitching event is detected 108.

[0058] If a switching event is detected 108, mode detection process 100places the system in the open mode of operation 110 and the system 20 ischanged over to a second system configuration 112 which has a secondsystem topology and performs a second set signal processing operationsthat is configured for play with the tailgate of the vehicle opened andthe primarily listening position outside of the vehicle, near the rearopening.

[0059] If another switching event 114 is detected, then the modedetection process 100 reverts the system 20 back to the conventionalmode of operation 104 and the system is placed in the first systemconfiguration 106.

[0060] In each system configuration, 106, 112, the system 20 has acertain system topology which defines how different signals provided byan audio source are routed to the various speakers in the system. In thefirst system configuration 106, the system topology is arranged in orderto better optimize the system for play with the doors of the automobileclosed and the primary listening in the seating area in the passengercompartment. Similarly, in the second system configuration 112, thesystem topology is arranged in order to better optimize the system forplay with a rear tailgate opened and the primary listening positionoutside the automobile near the rear opening. For example, in an audiosystem 20 having a speaker configuration similar to the arrangement inFIG. 1A and an audio source which produces 5.1 channels of audio data(i.e., front left, front right, front center, left surround, and rightsurround of full bandwidth (20-20 kHz) audio data plus a sixth channelof low frequency audio data), the first and second system configuration106, 112 may have a system topology as shown in Table I. TABLE I SystemTopology in Conventional Mode (i.e., speakers (shown in FIG. SystemTopology in Open Mode (i.e., 1A) which receive audio data in thespeakers (shown in FIG. 1A) which Audio Data Conventional mode) receiveaudio data in the Open mode) Front left audio data Front left speakers24b, 24d Rear left speaker 28b Front right audio data Front rightspeakers 24a, 24c Rear right speaker 28a Front center data Providedequally to front left and Provided equally to rear left and rear rightspeakers 24a-24d right speakers 28a-28b Left Surround audio data Sideleft speaker 26b and rear left Side left speaker 26b and front leftspeaker 28b speakers 24a, 24d Right Surround audio Side right speaker26a and rear right Side right speakers 26a and front data speaker 28aright speakers 24a, 24c Low Frequency data (i.e., Subwoofer speaker 29Subwoofer speaker 29 the .1 channel)

[0061] In other separate embodiments, many other speaker arrangementsand routing of audio data is possible. For example, an audio system mayhave a speaker arrangement as shown in FIG. 1B and may have an audiosource which produces 6.1 channels of audio data including a front left,front right, front center, left surround, right surround, and centersurround of full bandwidth (20-20 kHz) of audio data plus a sixthchannel of low frequency audio data. In this example, the systemconfiguration 106, 112 may have the system topology as shown in TableII. TABLE II System Topology in Conventional Mode (i.e., speakers (shownin FIG. System Topology in Open Mode (i.e., 1B) which receive audio datain the speakers (shown in FIG. 1B) which Audio Data Conventional mode)receive audio data in the Open mode) Front left audio data Front leftspeakers 24b, 24d Rear left speaker 28b Front right audio data Frontright speakers 24a, 24c Rear right speaker 28a Front center data Frontcenter speaker 25 Rear center speaker 23 Left Surround audio data Sideleft speaker 26b and rear left Side left speaker 26b and front leftspeaker 28b speakers 24a, 24d Right Surround audio Side right speaker26a and rear right Side right speakers 26a and front right data speaker28a speakers 24a, 24c Center Surround audio Center rear speaker 23Center front speaker 25 data Low Frequency data (i.e., Subwoofer speaker29 Subwoofer speaker 29 the .1 channel)

[0062] In other embodiments, a system configuration may include atopology in which one or more speakers are shut off in different modesof operation. For example, referring again to FIG. 1A, the front leftand right speakers 24 a-24 d may be shut off in the open mode of playleaving the side speakers to output left and right surround sound.Alternatively, the side speakers may be shut off in the open mode,leaving the front speakers to output the left and right surround sound.Similarly, the rear speakers 28 a-28 b may be shut off in theconventional mode leaving the side speakers to output the surroundsound.

[0063] Other embodiments may shut off front speakers 24 a-24 d (shown inFIG. 1) and side speakers 26 a-26 b in open mode. In this arrangement,left, right and center surround signals would be mixed with the left,right and center front signals that are fed to speakers 28 a-28 b.

[0064] In addition to changing the system topology in each mode ofoperation, the first and second system configuration 106, 112 alsoperform different signal processing operations in each mode. Signalprocessing operations may include operations such as equalization,amplification, signal mixing, spatial enhancement, dynamic range controland other signal processing techniques on one or more channels of audiodata in order to alter the frequency response (both magnitude and phaseas a function of frequency), polarity, and the magnitude of the voltagelevel of the signals delivered to each of the speaker channels in eachthe mode of operation.

[0065] The first and second system configurations 106, 112, may performdifferent equalization signal processing operations in order to providefor a different frequency response of the system 20 in each mode ofoperation. Equalization signal processing may be performed using any ofthe various techniques known in the art. For example, equalizationsignal processing may be performed on each channel of audio data bypassing the data through one or more digital filters whose filtercoefficients are stored in memory and provided to the digital signalprocessor. Sets of filter coefficients corresponding to each mode ofoperation would be stored in memory, and the system could switch sets ofcoefficients according to commands issued by the mode detection process100.

[0066] Equalization processing operations may also be implemented in theanalog domain by providing physically separate circuits with separatesets of filters for each mode of operation. Different circuits would beswitched into or out of the signal path in accordance with commandsissued by the mode control process 100. Alternatively, there may be onephysical circuit in which the performance can be dynamically adjustedthrough use of variable gain circuits, voltage controlled filters,switchable electrical component values, switched capacitor filters, orany other form of adjustable or programmable analog filters or signalprocessors.

[0067] Equalization signal processing operations, whether implemented inthe digital or analog domain, should be designed to provide a smootherfrequency response of the audio system in each mode of play as comparedto the frequency response of the system with no equalization.Furthermore, the frequency response of the system measured at thedesired listening position for the open mode of operation (outside ofthe vehicle in line with the open door or tailgate) should be smootherusing the signal processing designed for operation in the open mode thanthe response would be if the conventional mode signal processing wereused. For each mode of operation, the overall measured frequencyresponse of the system measured at each desired listening position willgenerally be similar in character. However, the frequency response ofthe signal processing used for each mode will generally be significantlydifferent. For purposes of discussion, it should be noted that we willsometimes refer to signal processing used for equalization as a ‘channelof equalization’ in this specification. The channel of equalization maybe accomplished using either analog or digital techniques. We will alsosometimes refer to the frequency response of the signal processing asthe ‘frequency response of the channel of equalization’.

[0068] First and second system configurations 106, 112, may includedifferent amplification processing operations of the audio signalsapplied to a speaker for each mode of operation. In other words, thefirst system configuration 106 may include signal processing operationswhich adjust the amplification of the audio signals in one manner, andthe second system configuration may include signal processing operationswhich adjust the amplification of the audio signals in a differentmanner. Adjusting the amplification of the audio signals may beperformed using any of the techniques known in the art. Adjusting gaincan be done in multiple places within the signal path of an audiosignal, and the system is not limited in the locations where gainadjustment occurs. For example, the amplification of an audio signalapplied to a speaker may be adjusted by changing the gain of anamplifier in the signal path of a particular speaker. In a digitalsystem, the gain for each channel for each mode of operation may bedetermined by a multiplication coefficient or set of filter coefficientsstored in memory and supplied to a digital signal processor in order tocontrol the level of the signal supplied to one or more speakers in eachmode of operation. The gain may also be adjusted in the analog domain bycontrolling a variable gain analog amplifier (or other known methods ofcontrolling gain in an analog system) located in the signal path of eachchannel of audio data.

[0069] The first and second system configurations 106, 112 may performdifferent signal mixing signal processing functions in each mode ofoperation. Signal mixing operations involve summing various signalstogether is various proportions. Mixing may occur in one or both modesof operation. Summing can be accomplished using op amp summer circuitryin the analog domain, or data values can be directly summed by amicroprocessor or digital signal processor.

[0070] The first and second system configuration 106, 112 may includedifferent spatial enhancement signal processing in each mode ofoperation. Spatial enhancement signal processing generally improves thespatial character of the sound field created by the system and may beimplemented using any of the techniques known in the art. One spatialenhancement technique for two-channel audio involves determining firstsum and difference signals by alternately adding and subtracting firstand second signals from each other (hereinafter referred to as a matrixoperation). Next, some form of signal processing is applied at least tothe difference signal (or possibly to both the sum and differencesignals, where the processing applied to the sum and difference signalsis different), then a second matrix operation (take sum and differenceof processed sum and difference signals) is performed to generate thirdand fourth signals. These third and fourth signals are now spatiallyenhanced versions of the first and second signals. Other enhancementtechniques might only operate on a difference signal. In these methods,a difference of two signals is taken. The difference signal is modifiedin some manner, then added back to one of the original channels andsubtracted from the other of the original channels.

[0071] In the open mode of operation, spatial enhancement may beperformed on the signals provided to the rear speakers (e.g., speakers28 a-28 b in FIG. 1A) since these speakers will most likely be theprimary speakers providing sound to listeners. Spatial enhancement maybe performed on the complete signals applied to the rear speakers, ormay be applied to only a portion of the signals applied to the rearspeakers. For example, for reproduction of a surround sound signalsource, center channel information may be applied to each rear speakerequally, without any spatial enhancement processing. Simultaneously,left and right channel signals may be applied to left and right speakersrespectively. These could be applied with or without spatial enhancementprocessing. Similarly, left and right surround signals could be appliedwith or without spatial enhancement processing to left and rightspeakers respectively, where the spatial enhancement processing usedcould either be the same as or different from that applied to the leftand right channel signals. In one particular embodiment, the secondconfiguration feeds center channel signals equally to rear speakers 28a-28 b (shown in FIG. 1A) without spatial enhancement, front left andright signals to left and right rear speakers 28 a-28 b respectivelywithout spatial enhancement, and spatially enhanced left and rightsurround signals to left and right rear speakers 28 a-28 b respectively.

[0072] Other combinations of performing spatial enhancement processingof various signals is also possible. For example, a system such as thatdescribed in co-pending application titled “Audio Signal Processing”having U.S. Ser. No. 09/886,868 filed on Jun. 21, 2001 and assigned toBose® Corporation, which is herein incorporated by reference, could beused in the rear of the vehicle, where spatial enhancement processing isused with the configuration of speakers disclosed.

[0073] It should be understood that spatial enhancement is not limitedto the second system configuration during the open mode of operation,but may also be performed on the audio signals provided to one or moresets of speakers (e.g., the front sets of speakers 24 a-24 b, 24 c-24 dor rear sets of speakers 26 a-b, 28 a-b shown in FIG. 1A) in firstsystem configuration during the conventional mode of operation.

[0074] It should be noted that other signal processing operations whichaffect system functions or performance attributes may change in theconventional and open mode of operation. For example, the dynamic rangeof the audio signal supplied to one or more speakers may be changeddepending on the mode of operation. Additionally, balance/fade settingsmay be changed depending on the operation (e.g., fade control may beshut off or set to some fixed position in the open mode).

[0075] Equalization processes, amplification, spatial enhancement,signal mixing, dynamic range adjustment, and other signal processes maytake place in either the digital domain with a device such as digitalsignal processor, microprocessor, digital amplifier, or other suitabledigital device, or in the analog domain with separate physical circuitsor a single physical circuit with dynamically adjustable elements (e.g.,variable gain amplifiers, voltage controlled filters, etc.).

[0076] Additionally, while a dual-mode audio system is illustrated inFIG. 2A, the concept may be extended to audio systems which operate inthree or more modes of operation. For example, as shown in FIG. 2B, anaudio system may have a first system configuration 154 (with a firsttopology and a first set of signal processing operations) in aconventional mode when all of the doors of the automobile are closed, asecond system configuration 162 (with a second topology and second setof signal processing operations) when one set of doors (e.g., a tailgateonly) are open, and a third system configuration 168 (with a thirdtopology and a third set signal processing operations) when a differentset of doors (e.g., a tailgate and a rear door) are open. When aswitching event occurs 156, 164, 170, mode detection process 150determines the proper mode of operation 152, 160, 166 based on the stateof a switch and/or the state of one or more physical conditions of theautomobile (e.g., whether doors are opened/closed, engine isoff/running, passenger in/out of driver's seat, etc.) and modifies theaudio data accordingly.

[0077] As shown in FIG. 3, audio system 20 also may include a batterymonitoring process 200 which may receive input 202 from the automobile10 that indicates whether the engine of the automobile is running, whichtells the audio system whether the primary power supply is theautomobile's battery or another power source such as an alternator.Numerous possible signals could be provided to indicate whether or notthe engine is running, such as a tachometer signal indicating the RPM ofthe engine (i.e., if RPM is zero, then the engine is not running andpower is being drawn primarily from the battery), a signal indicatingthe state of the ignition lock (i.e., if the ignition is locked then theautomobile is not running), or any of a number of digital signals thatmay be available on a communications bus which may be included in avehicle electrical system.

[0078] If the battery condition monitoring process 200 detects that theengine is running 203 (and thus power is not being primarily drawn fromthe battery), then there is no adjustment to the system configuration inorder to conserve battery power 204.

[0079] When the battery condition monitoring process 200 detects thatthe engine is not running 203 (and thus power is being primarily drawnfrom the battery), the system 20 may adjust system configuration (i.e.,system topology, signal processing operations or both) to conservebattery power 206 using a variety of techniques without substantiallydegrading system performance. For example, since the front speakers(e.g., 24 a-b, 24 c-24 d in FIG. 1A) consume power but do notappreciably affect system performance outside the rear of the vehicle,the system may be configured to shut off the front pair speakers whenoperating under battery power in open mode. Similarly, the rear speakers(28 a-28 b in FIG. 1A) may be shut off when operating in theconventional mode. Thus, it should be understood that the adjustment tosignal processes to conserve power 206 may differ depending on the modeof operation of the audio system 20. By adjusting system configurationin order to conserve power when the battery monitoring process detectsthat the engine is not running, the system is able to extend the lengthof time it may operate under battery power.

[0080] Speakers may be shut off in a variety of ways, including bymuting the output of the amplifier feeding a particular speaker, placingthe amplifier in a standby mode (many commercially-available amplifierintegrated circuits, such as the TDA 8567Q amplifier manufactured byPhilips® Semiconductor, are configured with both mute and standbymodes), reducing the audio signal fed into an amplifier to substantiallyzero, interrupting the signal path between an amplifier and a speaker,or removing power from an amplifier feeding a particular circuit orspeaker.

[0081] Since a significant amount of power is concentrated in the lowfrequency portion of music, the system may the raise cutoff frequencies(or increase the order of attenuation as a function of frequency, orboth) of high pass filters that may be located in the signal path of oneor more of the signals delivered to the speakers in order to conservepower.

[0082] Power may also be conserved by reducing the magnitude of thevoltage of the audio signal applied to one or more speakers. Onetechnique for reducing the magnitude of the voltage is to reduce thegain in the signal path of the audio signal (which can be done bychanging the gain of an amplifier, or the attenuation of a passiveattenuator in analog implementations, or by changing coefficients indigital filters or digital multiplication operations in digitalsystems). Another technique for reducing the magnitude of the voltage ofaudio signals is through the use of a dynamic range control device inthe signal path of the audio signal. A dynamic range control device is adevice which limits, compresses, expands or otherwise changes thedynamic range of an audio signal.

[0083] One use of dynamic range control devices in audio systems is tokeep a device (typically a power amplifier) from clipping its output. Adynamic range control device used in this type of application iscommonly known as a limiter and is configured to keep the maximumvoltage applied to the amplifier below a set minimum value under alloperating conditions.

[0084] Dynamic range control devices are typically constructed using avariable gain element (such as an amplifier in an analog implementationor a multiplier in a digital implementation), a control element, and asignal detector of some type (typically a level detector to detect,peak, average or RMS level of a signal, although other types ofdetectors are also possible), where the gain of the variable gainelement is varied as some function of the detected signal of interest bythe control element. The function defines the relationship between thegain of the variable gain element and the detected quantity of thesignal of interest. The nature of the function may change depending onthe detected quantity, or may remain constant over the entire range ofdetected values. For example, a threshold value for the detectedquantity may be determined, where the gain of the variable gain elementis not changed as long as the detected quantity remains below thethreshold value, but the gain is changed according to the specifiedfunction if the detected quantity exceeds the threshold level. Limiterswork by reducing the gain of the variable gain element when the sensedparameter of the signal exceeds some set threshold value, which isusually chosen to allow maximum output of a device (such as a poweramplifier) without clipping. Thus, in one embodiment the batterymonitoring process may reduce the maximum voltage of an audio signalapplied to one or more speakers by lowering the threshold value of alimiter when the battery monitoring process 200 detects that the audiosystem 20 is primarily running off of the battery.

[0085] Referring again to FIG. 3, the battery condition monitoringprocess 200 receives input 208 about various operating conditions of thebattery and estimates the approximate amount of energy remaining in thebattery, in order to ensure that there is sufficient charge remaining inthe battery to re-start the automobile. If the estimated batterycapacity reaches or falls below a predetermined threshold value, thenthe system 20 may notify the user that battery energy is getting low 210and may take further power conservations measures 212.

[0086] The battery condition monitoring process 200 receives input 208indicating various factors related to the current operating condition ofthe battery. These conditions may include the discharge currentmagnitude and rate, the accumulated time discharging has been occurring,the ambient temperature, battery output voltage, and other conditionsthat one skilled in the art might wish to monitor in order to estimatethe remaining capacity of the battery. From these conditions, process200 estimates the remaining capacity of the battery.

[0087] The voltage profile of a battery is the relationship between thebattery output voltage and the discharge conditions (length of time thebattery has been discharging, rate of discharge, magnitude of dischargecurrent, temperature). The output voltage of a secondary (re-chargeable)battery decreases over time according the discharge conditions.Batteries, like lead-acid batteries commonly used in automobiles, do nothave a singular discharge curve over all operating temperatures anddischarge currents. Rather, a particular battery's voltage profile curveis a function of the operating conditions described above. The set ofbattery voltage profile curves for a particular battery are readilyavailable from the manufacturer. Manufacturers also provide curvesshowing battery capacity as a function of operating conditions. Onetechnique for estimating the remaining capacity of the battery involvesdetermining where the battery is operating on its appropriate discharge(profile) curve, given the (monitored) operating conditions. From thisinformation and the capacity information available from themanufacturer, the remaining battery capacity can be estimated.

[0088] Another technique for estimating the remaining capacity of thebattery is to estimate the state of charge of the battery by measuringhow much energy is put into it during charging and how much energy isdrained from it when it is in use. This is sometimes called coulombcounting. In a separate embodiment, a battery monitoring process maymonitor the amount of current being discharged from the battery as wellas the amount of current that charges the battery and, from thesemeasurements, estimate the remaining charge in the battery.

[0089] When the estimated capacity reaches a predetermined value abovethe minimum level necessary for normal re-starting of the vehicle (whichis set as the battery capacity threshold value), the battery conditionmonitoring process 200 will inform the user 210 by issuing an alarm,which can be audible (e.g., output through the audio system) or visual(e.g., on a visual display) or tactile (e.g., actuate a vibrating devicesuch as a pager). In other separate embodiments, the battery conditionmonitoring process 200 may shut down the audio system or place thesystem in a standby (or sleep) mode in which all unnecessary components,including all amplifiers, are shut off when the estimated capacityreaches the battery capacity threshold value. Also, in a vehicleequipped with remote starting capability, a battery condition monitoringprocess may trigger the remote starting process to periodically startthe vehicle to recharge the battery when the estimated capacity reachesthe battery capacity threshold value.

[0090] In other separate embodiments, a battery condition monitoringprocess may have several predetermined thresholds which cause the systemto take different power conservation measures (e.g., shutting offspeakers, adjusting equalization, automatically starting the automobile,reducing the magnitude of voltage of the audio signals applied to aspeaker, placing the system in a standby mode, shutting off the system,etc.) at different predetermined thresholds.

[0091] In another embodiment, an audio system may include a batterymonitoring process which does not estimate the remaining capacity of thebattery, but which monitors one or more operating conditions of thebattery such as the discharge current, current drawn by the audiosystem, temperature, or the battery's voltage. The battery monitoringprocess which monitors the operating condition of the battery may takeone or more actions, such as triggering an alarm, reducing powerconsumption, placing the system in a standby mode, or completelyshutting down the system, if the operating condition of the batteryreaches a predetermined state. The predetermined state may be the stateof one or more of the monitored conditions such as the battery voltage,discharge current, and ambient temperature, or a combination ofconditions.

[0092] It should be noted that any number of the known techniques forestimating the remaining capacity of a battery or monitoring theoperating condition of a battery may be utilized in other embodimentsand the invention is not limited to the particular embodiments describedabove.

[0093] In other separate embodiments, an audio system may raise thecut-off frequencies of the high pass filters, shut off speakers, limitthe gain of the amplifiers, reduce the dynamic range of audio signals,or take other energy conservation measures either whenever operation onbattery power is detected (as shown in FIG. 2A), or when remainingbattery energy decreases to a predetermined threshold. It should beunderstood that a battery monitoring process may be implemented in adual mode audio system (as in audio system 20 shown in FIGS. 1A-B) or ina purely conventional audio system.

[0094] The circuitry implementing the mode selection, battery conditionmonitoring processes, and system configurations 100, 200, 106, 112, 206,210, 212 illustrated in FIGS. 2-3 may be implemented in hardware,software, firmware or the like in one or more locations in the audiosystem 20. For example, the circuitry for all of the processes may bephysically located in the front control console 21 or rear controlconsole 22 (in FIG. 1A) or the circuitry may be distributed acrossseveral devices of the system.

[0095] In a conventional vehicle audio system, the audio sources aretypically located in front of the vehicle or at least a controlinterface for the audio sources is located in the front. When the audiosystem is operating in the open mode, for convenience, the audio sourcesor at least a set of controls for the audio sources should be accessiblefrom the open tailgate (or door), which would normally be at the rear ofthe vehicle where the listeners would be located. As shown in FIG. 4, aduplicate set of user controls 80 is provided within the vehicle 10cabin near the opening of the rear tailgate 50. This may be a completeset of duplicate controls, such as source selection, volume, and sourcetransport controls (e.g., play, stop, pause, skip forward, skipbackwards, fast forward, fast reverse, preset selection, tune up ordown, etc.). Alternatively, the rear console may be some subset of thecomplete control interface present in the front of the vehicle.Additionally, FIG. 4 shows a set of speakers 64 mounted on the vehicle'stailgate 50 such that their primary axis of radiation 70 is directed atan angle of approximately 45 degrees relative to the plane of the groundon which the vehicle sits when the tailgate 50 is opened, and theprimary axis of radiation 70 substantially faces into the passengercompartment of the vehicle when the tailgate is closed.

[0096] An additional way of controlling the audio sources from the rearof the vehicle is to implement the control functions using a remotecontrol. A separate remote control may be used, or audio system controlfunctions could be integrated onto a vehicle key fob remote, similar tothose for remote keyless entry. Using a key fob remote, a plurality ofbuttons can be added to the key fob to provide limited audio functioncontrols such as volume and source selection. Alternatively, existingkey fob remote buttons that operate normal functions such as lock andunlock with the vehicle operating in conventional mode, can be re-mappedto operate audio functions when the vehicle is operating in open mode.Re-mapping could occur by activating a switch, button, or a sequence ofbuttons to change the remote function from normal vehicle functions toaudio system functions. For example, one method to do this is by addinga shift button that changes the functions of other buttons on theremote. Alternatively, the vehicle could sense the mode, and change itsinterpretation of the commands sent by the key fob remote. For example,lock and unlock could become volume up and down when the system wasoperating in open mode.

[0097] Additionally, one or more external audio system inputs may beprovided in the rear of the vehicle. For example, one input may beoptimized to accept the output of a microphone. In this case, additionalpre-amplification (and possibly a separate volume control) may berequired. This would allow the vehicle to be used as a portable publicaddress system. A line level input may also be provided. This wouldallow additional sources, such as a portable MP3 or CD player, to beconnected to the system and be easily accessible from the rear.

[0098] Other features may be included in a rear control panel. Forexample, when the vehicle is equipped with an integrated video source(DVD-video, VHS, etc), a video output jack can be made accessible fromthe rear of the vehicle, so a video display may be attached.

[0099] FIGS. 5A-5D illustrate several locations where rear speakers maybe mounted in order to provide high quality sound for both modes ofoperation. It should be noted that the speakers illustrated in FIGS.5A-5D may be upper frequency speakers (e.g., tweeters, mid-ranges), ormay be substantially full range speakers (which radiate sound over themajority of the audible frequency range of the human auditory system).Additionally, although speakers 60, 62, 64, and 66 shown in FIGS. 5A,5B, 5C, and 5D, respectively, are shown as individual transducers, itshould be understood that the speakers may also be mounted withinenclosures.

[0100] The primary axis of radiation of a speaker is the direction inwhich the speaker radiates maximum energy over the majority of itsoperating range. This direction is typically in line with physicalcenter axis of symmetry of an axi-symmetric transducer. For ease ofunderstanding, axi-symmetric transducers are assumed to be used here,and the axis of primary radiation is assumed to be aligned with thecenter axis of symmetry of the transducer and points away from the frontsurface of the primary radiating surface of the transducer, where thefront surface is the surface that is coupled to the listeningenvironment. It should be noted, however, that the invention is notlimited to use of axi-symmetric transducers. The orientations describedcan be adjusted as needed such that sound radiation is directed in thedesired directions.

[0101] As shown in FIG. 5A, an automobile 10 includes a rear tailgate 50having an upper hinge 51 which is shown as open. A pair of rear speakers60 (e.g., mid-range speakers) are mounted within the automobile cabinnear the opening of the tailgate 50 such that the pair of speakers 60are outwardly directed from the cabin when the tailgate 50 is opened.When the tailgate 50 is closed, sound from speaker pair 60 is reflectedoff of the tailgate back into the automobile cabin. There are numerouslocations in the rear portion of the cabin of the automobile wherespeakers 60 may be mounted and the invention is not limited to thespecific location illustrated in FIG. 5A. Additionally the speaker pair60 may be oriented such that they do not point directly at the tailgate50 when the tailgate is closed, but may be angled with respect to thetailgate 50. For example, in separate embodiments, speaker pair 60 maybe mounted on the cabin floor, cabin ceiling, cabin sidewalls, rearcabin deck, or back of the rearmost seat in the automobile 10. Finally,an additional speaker, such as a subwoofer, may also be mounted withinthe passenger compartment near the tailgate.

[0102] FIGS. 5B-5C illustrate additional separate embodiments of wherepairs of rear speakers may be mounted on an automobile 10 having atailgate 50. Specifically, FIG. 5B shows a pair of rear speakers 62mounted within the automobile cabin near the top hinge 51 of thetailgate 50.

[0103]FIG. 5C shows a pair of rear speakers 64 mounted on the tailgate50 such that the left speaker is located in the upper left-hand side ofthe tailgate and a right speaker is located in the upper right-hand sideof the tailgate. The speakers 64 may be mounted within the trim of thetailgate 50. The speakers may also be mounted on a window on thetailgate 50 using methods similar to those used to attach a rear viewmirror to a front windshield. The window mounted speakers mayadditionally be attached to the trim surrounding the window foradditional structural support. The pair of rear speakers 64 are alsooriented such that the primary axis of radiation 70 of the speakers 64face substantially towards the rear of the automobile 10 and are angledat an angle of approximately 45 degrees relative to a plane parallel tothe ground when the tailgate is open. Similarly, the primary axis ofradiation 70 of the speakers 64 is pointed substantially towards thepassenger cabin when the tailgate is closed. This speaker orientationmay be particularly advantageous because it directs sound into thevehicle when the tailgate is closed and also outwardly directs soundfrom the vehicle when the tailgate is open. Thus, this speakerorientation is particularly well-suited for accommodating both modes ofoperation of the audio system.

[0104]FIG. 5D shows another pair of rear speakers 66 mounted on thetailgate 50 roughly midway between the upper hinge 51 and lower edge 52of the tailgate 50. While this speaker orientation is well-suited foroperation in the conventional mode of operation because sound isdirected into the passenger cabin when the tailgate is closed, thisorientation may not be optimal for listeners that are located behind theautomobile 10, away from the tailgate, as these listeners will besignificantly off-axis to the main axis of radiation of the speakers 66.

[0105] While FIGS. 5A-5D illustrate various locations of a single pairof rear speakers, additional separate embodiments may include audiosystems where multiple pairs of rear speakers are mounted at multiplelocations in automobile cabin and tailgate. Additionally, note thatspeakers 60, 62, 64, and 66 shown in FIGS. 5A, 5B, 5C and 5D,respectively, represent a pair of speakers symmetrically located withinthe automobile, where the axis of symmetry is the centerline of theautomobile 10.

[0106] A number of embodiments have been described, however, it isevident that those skilled in the art may make numerous modifications ofthe departures from the specific apparatus and techniques disclosedherein without departing from the inventive concepts. Consequently, theinvention is to be construed as embracing each and every novel featureand novel combination of features present in or possessed by theapparatus and techniques disclosed herein and limited solely by thespirit and scope of the appended claims.

What is claimed is:
 1. A method for operating an audio system in anautomobile having a plurality of doors, the audio system including at anaudio source that produces a plurality of audio signals, the methodcomprising the steps of: implementing a first system configuration;receiving input indicating a change in operating mode; and in responseto input indicating a change in operating mode, implementing a secondsystem configuration which is different from the first systemconfiguration, wherein the second system configuration is implementedwhen one of the doors of the automobile is open.
 2. The method of claim1, wherein one of the doors of the automobile is a tailgate and whereinimplementing a second system configuration occurs when the tailgate isopened.
 3. The method of claim 2, wherein performing the second systemconfiguration occurs when the tailgate is closed.
 4. The method of claim1, further comprising the steps of: receiving an input indicating thatthe automobile's engine is not running; and in response to the inputindicating that the automobile's engine is not running, adjusting thefirst or second system configuration in order to reduce powerconsumption of the system.
 5. The method of claim 1, wherein the audiosystem further includes a plurality of loudspeakers and the step ofimplementing a first system configuration comprises implementing a firstsystem topology; and the step of implementing a second systemconfiguration comprises implementing a second system topology which isdifferent from the first system topology.
 6. The method of claim 1,wherein the audio system further includes a plurality of loudspeakers,and the step of implementing a second system configuration comprisesturning off one or more of the plurality of speakers.
 7. The method ofclaim 6, wherein the audio system includes an amplifier which providesan audio signal to one or more loudspeakers, and the step of turning offone or more of the loudspeakers comprises one of the following steps:muting the output of the amplifier, placing the amplifier in standbymode, reducing the voltage of the audio signal input to the amplifier toapproximately zero, disconnecting the one or more loudspeakers from theamplifier, or removing electrical power from the amplifier.
 8. Themethod of claim 1, wherein the step of implementing a first systemconfiguration comprises performing a first set of signal processingoperations on the plurality of audio signals and the step ofimplementing a second system configuration comprises performing a secondset of signal processing operations on the plurality of audio signals,wherein the first set of signal processing operations are different fromthe second set of signal processing operations.
 9. The method of claim5, wherein the audio source generates at least a left channel of audiodata, a right channel of audio data, a left surround channel of audiodata, and a right surround channel of audio data, and the audio systemfurther includes at least a pair of front speakers located near thefront of the passenger compartment in the automobile and a pair of rearspeakers located near the rear of the passenger compartment in theautomobile, and wherein the first system topology comprises: providingthe left and right channels of audio data to the front pair of speakers;and providing the left and right surround channels of audio data to therear pair of speakers; and wherein the second system topology comprises:providing the left and right channels of audio data to the rear pair ofspeakers.
 10. The method of claim 9 wherein the second system topologyfurther comprises providing the left and right surround channels ofaudio data to the front pair of speakers.
 11. The method of claim 1wherein the step of implementing the first system configurationcomprises: performing a set of equalization processes having a firstfrequency response on the plurality of audio signals; and wherein thestep of implementing the second system configuration comprises:performing a set of equalization processes having a second frequencyresponse on the plurality of audio signals.
 12. The method of claim 11wherein performing a set of equalization processes having a firstfrequency response comprises: sending one or more of the plurality ofaudio signals through a high pass filter having a first cutofffrequency; and wherein performing a set of equalization processes havinga second frequency response comprises: sending one or more of theplurality of audio signals through a high pass filter having a secondcutoff frequency.
 13. The method of claim 4 wherein the step ofadjusting the first or second system configuration to reduce powerconsumption comprises changing one or more signal processing operationsin the first or second system configuration.
 14. The method of claim 13,wherein the each of the plurality of audio signals are associated with asignal path, and the step of changing one or more signal processingoperations in the first or second system configuration comprisesreducing the gain in one or more of the signal paths.
 15. The method ofclaim 13, wherein the step of changing one or more signal processingoperations in the first or second system configuration comprisescontrolling the maximum output power level of the audio system.
 16. Themethod of claim 15, wherein the audio system includes a plurality ofvariable gain elements and the step of controlling the maximum outputpower level comprises: receiving one or more audio signals from theaudio source; detecting the level of one or more audio signals; anddynamically adjusting the gain of one or more variable gain elements asa function of the detected level of the one or more audio signals. 17.The method of claim 4 wherein the system further includes a plurality ofloudspeakers and the step of adjusting the first or second systemconfiguration to reduce power consumption comprises turning off one ormore of the loudspeakers in the first or second system configuration.18. The method of claim 17 wherein the audio system includes anamplifier which provides an audio signal to one or more loudspeakers,and the step of turning off one or more of the loudspeakers comprise oneof: muting the output of the amplifier placing the amplifier in standbymode, reducing the voltage of the audio signal input into the amplifierto approximately zero, disconnecting the one or more loudspeakers fromthe amplifier, or removing electrical power from the amplifier.
 19. Themethod of claim 8, wherein the audio system further includes a pluralityof variable gain elements and the step of performing first sets ofsignal processes comprises: receiving one or more audio signals from theaudio source; detecting the level of one or more audio signals; anddynamically adjusting the gain of one or more variable gain elements asa function of the level of the one or more audio signals; and whereinthe step of performing the second set of signal processes comprises:receiving one or more audio signals from the audio source; detecting thelevel of one or more audio signals; and dynamically adjusting the gainof one or more variable gain elements as a function of the level of theone or more audio signals, where the function used in the second set ofsignal processes is different from the function used in the first set ofsignal processes.
 20. The method of claim 8, wherein each of theplurality of audio signals have an associated signal path and the stepof performing first and second sets of signal processes comprises:receiving one or more audio signals from the audio source; and adjustingthe gain of one or more signal paths; and wherein the step of performingthe second set of signal processes comprises: receiving one or moreaudio signals from the audio source; and adjusting the gain of one ormore signal paths, wherein the gain of one or more signal paths in thesecond set of signal processes is different from the gain of the sameone or more signal paths in the first set of signal processes.
 21. Themethod of claim 8 wherein the audio system further includes a pluralityof equalization processes, and the step of performing a second set ofsignal processing operations comprises: receiving one or more audiosignals from the audio source; and adjusting the frequency response ofthe equalization process performed on one or more of the audio signalsreceived from the audio source.
 22. The method of claim 8, wherein theaudio system further includes a plurality of loudspeakers and the stepof performing a second set of signal processing operations comprises:receiving a plurality of audio signals from an audio source; performingspatial enhancement signal processing on a group of the audio signals;and transmitting one or more spatially enhanced audio signals to a firstset of the plurality of the loudspeakers.
 23. The method of claim 8,wherein the step of performing a first set of signal processingoperations comprises: receiving one or more audio signals from the audiosource; performing first spatial enhancement signal processing on one ormore sets of the received audio signals; and wherein the step ofperforming a second set of signal processing operations comprises:performing second spatial enhancement signal processing on one or moresets of received audio signals, wherein first and second spatialenhancement signal processing operations are different.
 24. The methodof claim 1, wherein the step of receiving input indicating a change inoperating mode comprises: monitoring one or more physical conditions ofthe automobile; and generating a switch command based on a change in oneor more of the monitored physical conditions.
 25. The method of claim24, wherein one or more of the monitored physical conditions includesone of the following: whether a door is open, whether the automobile'sengine is running, or whether an occupant is present within theautomobile passenger compartment.
 26. The method of claim 1, wherein thestep of receiving input indicating a change in operating mode comprises:providing a switch accessible to a user, the switch having at least twostates; and receiving an input based on the state of the switch.
 27. Themethod of claim 26, wherein the switch is located near the rear of theautomobile within the passenger compartment.
 28. The method of claim 26,wherein the switch is located on a remote control device.
 29. The methodof claim 28, wherein the remote control device is a key fob.
 30. Themethod of claim 1, further comprising the steps of: monitoring one ormore operating conditions of the battery; and causing the audio systemto take an action based on one or more of the monitored operatingconditions of the battery.
 31. The method of claim 30, wherein the stepof causing the audio system to take an action based on the monitoredoperating conditions of the battery comprises: comparing one or more ofthe monitored operating conditions of the battery to a predeterminedstate; and if one or more of the monitored operating conditions reachesthe predetermined state, then triggering an alarm.
 32. The method ofclaim 31, wherein the alarm is an audible alarm, visual alarm, ortactile alarm.
 33. The method of claim 30, wherein the step of causingthe audio system to take an action based on one or more of the monitoredoperation conditions of the battery comprises: comparing one or more ofthe monitored operating conditions of the battery to a predeterminedstate; and if one or more of the monitored operating conditions reachesthe predetermined state, then reducing the power consumption of theaudio system.
 34. The method of claim 33 wherein the audio systemfurther includes a plurality of equalization processes, and the step ofreducing the power consumption of the audio system comprises: receivingone or more audio signals from an audio source; and adjusting one ormore equalization process applied to one or more audio signals to changethe frequency response of the audio system.
 35. The method of claim 34,wherein one of the plurality of equalization processes includes a highpass filter having a cutoff frequency, and the step of adjusting one ormore equalization processes comprises raising the cutoff frequency ofthe high pass filter.
 36. The method of claim 34, wherein one of theplurality of equalization processes includes a high pass filter, and thestep of adjusting the equalization processes comprises adjusting theorder of the high pass filter.
 37. The method of claim 33, wherein eachof the plurality of audio signals have an associated signal path, andthe step of reducing the power consumption of the audio system comprisesreducing the gain in one or more of the audio signal paths.
 38. Themethod of claim 33, wherein the audio system further includes aplurality of variable gain elements and the step of reducing the powerconsumption of the audio system comprises: receiving one or more audiosignals from the audio source; detecting the level of one or more of theaudio signals, and dynamically adjusting the gain of one or morevariable gain elements as a function of the detected level of the one ormore audio signals.
 39. The method of claim 33 wherein the systemfurther includes a plurality of loudspeakers and the step of reducingthe power consumption of the audio system comprises turning off one ormore of the loudspeakers.
 40. The method of claim 39 wherein the audiosystem includes an amplifier which provides an audio signal to one ormore loudspeakers, and the step of turning off one or more of theloudspeakers comprises one of the following steps: muting the output ofthe amplifier, placing the amplifier in standby mode, reducing thevoltage of the audio signal input into the amplifier to approximatelyzero, disconnecting the one or more loudspeakers from the amplifier, orremoving electrical power from the amplifier.
 41. The method of claim30, wherein the step of causing the audio system to take an action basedon the monitored operating conditions of the battery comprises:comparing one or more monitored operating conditions of the battery to apredetermined state; and if the monitored operating conditions reachesthe predetermined state, then shutting off the audio system.
 42. Themethod of claim 30, wherein the step of taking an action based on theone or more monitored operating conditions of the battery comprises:comparing one or more of the monitored conditions of the battery to apredetermined state; and if the monitored condition of the batteryreaches the predetermined state, then causing the automobile to startits engine.
 43. The method of claim 30, further comprising: estimatingthe remaining capacity of the battery based on one or more of themonitored operating conditions of the battery.
 44. The method of claim43, wherein the step of causing the audio system to take an action basedon the monitored battery condition comprises: comparing the estimatedremaining capacity of the battery to a predetermined value; and if theestimated battery capacity is equal to or less than the predeterminedvalue, then triggering an alarm.
 45. The method of claim 44, wherein thealarm is an audible alarm, visual alarm, or tactile alarm.
 46. Themethod of claim 43, wherein the step of causing the audio system to takean action based on the monitored battery condition comprises: comparingthe estimated capacity of the battery to a predetermined value; and ifthe estimated battery capacity is equal to or less than thepredetermined value, then reducing the power consumption of the audiosystem.
 47. A method for remote control of an audio system in anautomobile, comprising: providing a key fob having a plurality ofbuttons; defining a first set of commands corresponding to each buttonfor the plurality of buttons, wherein first set of commands includes acommand causing the automobile to actuate its door locks; defining asecond set of commands corresponding to one or more of the plurality ofbuttons, wherein the second set of commands includes one or morecommands for controlling the audio system of the automobile; andswitching between the first set of commands and the second set ofcommands based on a predetermined condition.
 48. The method of claim 47,wherein the key fob further includes a switch having two states, and thepredetermined condition is a state of the switch.
 49. The method ofclaim 47, wherein the audio system comprises a first mode of operationand a second mode of operation and wherein the predetermined conditionis the state of the mode of operation of the audio system, such that thefirst set of commands are valid when the audio system is in the firstmode of operation and the second set of commands are valid when theaudio system is in the second mode of operation.
 50. A method foroperating an audio system in a vehicle with a battery, the methodcomprising: monitoring one or more operating conditions of the battery;comparing one or more of the monitored conditions of the battery to apredetermined state; and if one or more of the monitored operatingconditions of the battery reaches the predetermined state, thentriggering an alarm.
 51. The method of claim 50 wherein the alarmcomprises a audible alarm, visual alarm, or tactile alarm.
 52. Themethod of claim 50, wherein monitoring one or more operating conditionsof the battery comprises one or more of following: sensing the outputvoltage level of the battery, sensing the discharge current of thebattery; or sensing the ambient temperature.
 53. A method for operatingan audio system in a vehicle with a battery, the method comprising:monitoring one or more operating conditions of the battery; andcomparing one or more of the monitored conditions of the battery to apredetermined state; and if one or more of the monitored operatingconditions of the battery reaches the predetermined state, then causingthe automobile to start its engine.
 54. The method of claim 53, whereinmonitoring one or more operating conditions of the battery comprises oneor more of following: sensing the output voltage level of the battery,sensing the discharge current of the battery; or sensing the ambienttemperature.
 55. A method for operating an audio system having aplurality of speakers in a vehicle with a battery, the methodcomprising: monitoring one or more operating conditions of the battery;comparing one or more of the monitored conditions of the battery to apredetermined state; and if one or more of the monitored operatingconditions of the battery reaches the predetermined state, then turningoff a subset of the plurality of speakers.
 56. The method of claim 55,wherein the step of monitoring one or more operating conditions of thebattery comprises one or more of following: sensing the output voltagelevel of the battery, sensing the discharge current of the battery; orsensing the ambient temperature.
 57. The method of claim 55, wherein theaudio system further comprises a plurality of amplifiers and each of theplurality of speakers is supplied an audio signal provided by one of theplurality of amplifiers, and wherein the step of turning off a subset ofthe plurality of speakers comprises one of the following steps: mutingthe output of an amplifier supplying an audio signal to a speaker,placing an amplifier supplying an audio signal to a speaker in standbymode, reducing the voltage of the audio signal input into an amplifiersupplying an audio signal to a speaker to approximately zero,disconnecting the one or more loudspeakers from an amplifier, orremoving electrical power from one or more amplifiers.
 58. A method foroperating an audio system having one or more equalization signalprocesses in a vehicle with a battery, the method comprising: monitoringone or more operating conditions of the battery; comparing one or moreof the monitored conditions of the battery to a predetermined state; andif one or more of the monitored operating conditions of the batteryreaches the predetermined state, then adjusting one or more ofequalization signal processes to change the frequency response of theaudio system.
 59. The method of claim 58, wherein one of theequalization processes includes a high pass filter having a cutofffrequency, and the step of adjusting one or more of the equalizationprocesses comprises raising the cutoff frequency of the high passfilter.
 60. The method of claim 58, wherein monitoring one or moreoperating conditions of the battery comprises one or more of following:sensing the output voltage level of the battery, sensing the dischargecurrent of the battery; or sensing the ambient temperature.
 61. A methodfor operating an audio system having one or more variable gain elementsin a vehicle with a battery, the method comprising: monitoring one ormore operating conditions of the battery; comparing one or more of themonitored conditions of the battery to a predetermined state; and if oneor more of the monitored operating conditions of the battery reaches thepredetermined state, then detecting the level of one or more of audiosignals received from an audio source, and dynamically adjusting thegain of one or more variable gain elements as a function of the level ofone or more audio signals received from an audio source.
 62. The methodof claim 61, wherein monitoring one or more operating conditions of thebattery comprises one or more of following: sensing the output voltagelevel of the battery, sensing the discharge current of the battery; orsensing the ambient temperature.
 63. A method for operating an audiosystem having a plurality of speakers in a vehicle with a battery, themethod comprising: monitoring one or more operating conditions of thebattery; estimating the remaining capacity of the battery based on oneor more of the monitored operating conditions of the battery; comparingthe estimated remaining capacity of the battery to a predeterminedvalue; and if the estimated remaining capacity of the battery is equalto or less than a predetermined value, then causing the audio system totake an action.
 64. The method of claim 63, wherein causing the audiosystem to take an action comprises triggering an alarm indicating thatbattery capacity is becoming low.
 65. The method of claim 63, whereincausing the audio system to take an action comprises causing theautomobile to start the engine.
 66. The method of claim 63, whereincausing the audio system to take an action comprises reducing the powerconsumption of the audio system.
 67. The method of claim 66, whereinreducing the power consumption of the audio system comprises turning offone or more loudspeakers.
 68. The method of claim 66, wherein reducingpower consumption of the audio system comprises turning off the system.69. The method of claim 66, wherein the audio system includes aplurality of equalization processes, and reducing power consumption ofthe audio system comprises: receiving an audio signal from an audiosource; and adjusting one or more equalization processes applied to oneor more audio signals to change the frequency response of the audiosystem.
 70. A method for operating an audio system in an automobilehaving a battery and an engine, wherein the audio system includes anaudio source that produces a plurality of audio signals and a pluralityof loudspeakers, the method comprising: determining whether the engineis running; and in response to the system determining that the engine isnot running, then changing one or more signal processes to reduce powerconsumption of the audio system.
 71. The method of claim 70, whereinreducing the power consumption of the audio system comprises turning offone or more loudspeakers.
 72. The method of claim 71, wherein the audiosystem includes an amplifier which provides an audio signal to one ormore loudspeakers, and the step of turning off one or more of theloudspeakers comprises one of the following steps: muting the output ofthe amplifier, placing the amplifier in standby mode, reducing thevoltage of the audio signal input into the amplifier to approximatelyzero, disconnecting the one or more loudspeakers from the amplifier, orremoving electrical power from the amplifier.
 73. The method of claim70, wherein the step of reducing power consumption of the audio systemcomprises turning off the system.
 74. The method of claim 70, whereinsaid audio system includes one or more equalization processes, and thestep of causing the audio system to take an action based on themonitored operating condition of the battery comprises: receiving one ormore audio signals from an audio source; and adjusting one or more ofthe equalization processes performed on one or more of the receivedaudio signals to change the frequency response of the audio system. 75.The method of claim 70, wherein the audio system further includes aplurality of variable gain elements and the step of reducing the powerconsumption of the audio system comprises: receiving one or more audiosignals from the audio source; detecting the level of one or more of theaudio signals, and dynamically adjusting the gain of one or morevariable gain elements as a function of the level of the one or moreaudio signals.
 76. The method of claim 70, wherein each of the pluralityof audio signals have an associated signal path, and the step ofreducing the power consumption of the audio system comprises reducingthe gain in one or more of the signal paths.
 77. An audio system for anautomobile having a plurality of doors and a battery comprising: anaudio input source; a plurality of loudspeakers; a first set ofoperating conditions for a first mode of operation; a second set ofoperating conditions for a second mode of operation, wherein the secondset of operating conditions is different from the first set of operatingconditions and occurs when one of the doors of the automobile is open;and a switch for changing between the first and second set of operatingconditions.
 78. The audio system of claim 77, wherein one of the doorsof the automobile is a tailgate and the first set of operatingconditions are configured for play while the tailgate is closed andlisteners are within the automobile and the second set of operatingconditions are configured for play while the tailgate is open andlisteners are outside the automobile.
 79. The audio system of claim 77,further comprising at least one channel of equalization, wherein thefirst set of operating conditions defines a first frequency response ofthe channel of equalization and the second set of operating conditionsdefines a second frequency response of the channel of equalization. 80.The audio system of claim 77, further comprising: a dynamic rangecontrol device configured to receive an audio signal having a firstdynamic range and output an audio signal having a second dynamic range,wherein the second dynamic range is different than the first dynamicrange.
 81. The system of claim 80, wherein the dynamic range controldevice comprises: a variable gain element; a signal level detector; anda control element, wherein the control element varies the gain of thevariable gain element as a function of the detected signal level. 82.The audio system of claim 77, wherein the first set of operatingconditions provides for a first system topology and the second set ofoperating conditions provides for a second system topology.
 83. Theaudio system of claim 77 further comprising: at least one inputindicating an operating condition of the battery; and a monitoringprocess coupled to the at least one input indicating the operatingcondition of the battery.
 84. The audio system of claim 83 wherein themonitoring process is configured to trigger an alarm if the monitoredoperating condition of the battery the reaches a predetermined state.85. The audio system of claim 83 wherein the monitoring process isconfigured to cause the audio system to implement a third set ofoperating conditions if the monitored operating condition of the batterythe reaches a predetermined state.
 86. The audio system of claim 85wherein the third set of operating conditions is configured to reducethe power consumption of the audio system.
 87. The audio system of claim83, wherein the monitoring process is configured to estimate theremaining capacity of the battery.
 88. The audio system of claim 85wherein the monitoring process is configured to trigger an alarm if theestimated remaining capacity of the battery reaches a predeterminedstate.
 89. The audio system of claim 77, wherein the switch is manuallycontrolled by a user.
 90. The audio system of claim 77, furthercomprising input indicating a change in a one or more physical operatingconditions of the automobile and wherein the switch is controlled by achange in one or more physical operating conditions of the automobile.91. The audio system of claim 90, wherein one or more of the physicaloperating conditions of the automobile is whether a door is opened orclosed.
 92. The audio system of claim 91 wherein the door is a tailgate.93. The audio system of claim 77, wherein the system further comprises:a rear control panel located within the passenger compartment of theautomobile towards the back of the automobile, the rear control panelcomprises one or more controls for operating the audio system.
 94. Theaudio system of claim 93, wherein the rear control panel furthercomprises a switch for changing between the first and second set ofoperating conditions.
 95. The audio system of claim 93, wherein the oneor more controls for operating the audio system comprise at least one ormore of the following: a volume control, a source selection control, ora source transport control.
 96. The audio system of claim 93, whereinthe rear control panel further comprises at least one pair of externalaudio source line level inputs.
 97. The audio system of claim 93,wherein the rear control panel further comprises external a microphonelevel input.
 98. The audio system of claim 97, wherein said rear controlpanel further includes a separate volume control for controlling thelevel of the external microphone input.
 99. The audio system of claim93, wherein the audio system further comprises an integrated videosource and the rear control panel further comprises a separate videooutput jack for connection to a video display.
 100. An audio system foran automobile having a passenger compartment and a tailgate hingidlyconnected to the top portion of the automobile's frame comprising: afirst speaker set comprising a first speaker and a second speakermounted on the tailgate of the automobile, wherein each speaker in thefirst set of speakers direct sound along a primary axis of radiation andhave a fixed orientation such that each speaker's primary axis ofradiation directs sound substantially towards the passenger compartmentof the automobile when the tailgate is closed, and the speaker's primaryaxis of radiation is pointed away from the passenger compartment of theautomobile and is angled relative to the plane of the ground when thetailgate is opened.
 101. The audio system of claim 100 wherein the angleis approximately 45 degrees relative to the plane of the ground when thetailgate is opened.
 102. The audio system of claim 100, wherein theprimary axis of radiation is directed into the passenger compartment atan angle that is approximately 45 degrees relative to the plane of theground when the tailgate is closed.
 103. The audio system of claim 100,wherein the first speaker set is located near an upper edge of thetailgate.
 104. The audio system of claim 100, wherein the tailgateincludes a window, and wherein the first speaker set is mounted on thetailgate window.
 105. The audio system of claim 100 wherein the audiosystem further comprises a first mode of operation configured for playwhile the tailgate is closed and listeners are within the automobile anda second mode of operation configured for play while the tailgate isopened and listeners are outside the automobile near the rear of theautomobile.
 106. The audio system of claim 105, further comprising asecond set of speakers comprising a first and second speaker, eachspeaker having primary axis of radiation that is pointed substantiallytowards the rear of the automobile and which direct sound outside theautomobile in the second mode of operation.
 107. An audio system for anautomobile having a passenger compartment and a tailgate hingidlyconnected to the automobile's frame and a rear seat or seats having afront portion and a rear portion: a first speaker set comprising a firstspeaker and a second speaker mounted on the rear portion of the rearseat or seats, wherein each speaker in the first set of speakers directssound along a primary axis of radiation and have a fixed orientationsuch that each speaker's primary axis of radiation directs soundsubstantially away from the passenger compartment of the automobiletowards the tailgate when the tailgate is closed, and the speaker'sprimary axis of radiation is pointed away from the passenger compartmentof the automobile and directs sound out of the rear of the automobilewhen the tailgate is opened.
 108. An audio system for an automobilehaving a rear seat, a passenger compartment with a floor, and a tailgatehingidly connected to the automobile's frame: a first speaker setcomprising a first speaker and a second speaker mounted on the floor,wherein each speaker in the first set of speakers directs sound along aprimary axis of radiation and have a fixed orientation such that eachspeaker's primary axis of radiation directs sound substantially awayfrom the passenger compartment of the automobile towards the tailgatewhen the tailgate is closed, and the speaker's primary axis of radiationis pointed away from the passenger compartment of the automobile anddirects sound out of the rear of the automobile when the tailgate isopened.
 109. An audio system for an automobile having a rear seat, apassenger compartment with a ceiling, and a tailgate hingidly connectedto the automobile's frame: a first speaker set comprising a firstspeaker and a second speaker mounted on the ceiling, wherein eachspeaker in the first set of speakers directs sound along a primary axisof radiation and have a fixed orientation such that each speaker'sprimary axis of radiation directs sound substantially away from thepassenger compartment of the automobile towards the tailgate when thetailgate is closed, and the speaker's primary axis of radiation ispointed away from the passenger compartment of the automobile anddirects sound out of the rear of the automobile when the tailgate isopened.
 110. An audio system for an automobile having a passengercompartment with a ceiling, floor, and sidewalls, and having a rearopening comprising: a first speaker set comprising a first speaker and asecond speaker mounted within the passenger compartment in the rear halfof the automobile, wherein each speaker in the first set of speakersdirect sound along a primary axis of radiation and have a fixedorientation such that each speaker's primary axis of radiation directsound substantially towards rear opening of the automobile and whereinthe neither speaker in the first speaker set is mounted on a sidewall ofthe passenger compartment.
 111. The audio system of claim 110 whereinthe first set of speakers is mounted on the ceiling within the passengercompartment.
 112. The audio system of claim 110 wherein the first set ofspeakers is mounted on the floor within the passenger compartment.